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i have finished steps 1,2,3,and 4 got +5V ,-5V pulse width of 400us pulse period of 8ms , i was getting voltage spikes but think i must have shorted something out just wondering what to look for what parts are likely to be faulty to get 350V or higher in step 4 . I have looked for any obvious shorts and checked my damping resistor jig ok there but might have accidentally shorted something or maybe just have a faulty part please advise anything that may help. as i have only a little electronics knowledge. Please help Graham.
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Do you have your coil connected?Originally posted by Graham View Post -
Hi Graham,
Please post some pictures of your setup and pcb top/bottom. It often helps troubleshooting a lot.Comment
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Fixed problem with flyback voltage had damping resistor connected wrong step5 shoe polish tin didn't seem to have a noticeable affect step 6 think i have a faulty 100k trimmer no effect sorry cant send pics at the moment don't have a camera hope to replace trimmer soon cross fingers thats whats wrong want to go beach detecting close to retirement all the best any thoughts Graham.Comment
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Changed 100K trimmer seems to work ok now but having difficulty setting damping jig to get the right resistance from oscilloscope wave currently using Hantek 6022be maybe i need a better oscilloscope. will keep you updated now onto the next step as soon as i get the right resistance. GrahamComment
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I've noticed that people tend to over-think the damping resistor issue, especially when using the damping resistor tool. If you're simply trying to get the thing working, make a jumble-wound mono coil with an inductance between 300uH and 400uH. You can usually critically damp the coil using either a 680R, 470R, or 330R resistor (depending on the detector). Once you have the detector working, you can then play around with different coils and adjust the damping resistor more accurately if necessary.Originally posted by Graham View PostComment
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As George is saying, the damping resister is not that critical for starting off.
What could be happening is that your coil might be interacting with something metal (in, under, around) your table or test setup.
Hang it up in the air or use a high cardboard box. My coils were reacting to some hidden iron nails in the table.
Later on I found that I had to hang them at a height of around 160cm to avoid detecting steel girders in floor or ceiling.
Yes, the MPP is very sensitive!Comment
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I had a short checked some signal diodes while in circuit 2 of them seemed to be faulty will replace them in MPP and hope no other parts were affected like capacitors ic's or resistors will let you know how i go GrahamComment
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Finally go Mpp Detector working up to stage 7 i am looking forward to finishing it for me it has been a steep learning curve using an oscilloscope etc Not Sure how to connect stereo headphone yet isn't it set up for mono also i am wanting to know how a 5K taper for volume control would connect up any help appreciated GrahamComment
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sorry i still havn't got a camera but Managed to Finally get Mpp Detector working up to stage 7 i am looking forward to finishing it for me it has been a steep learning curve using an oscilloscope etc Not Sure how to connect stereo headphone yet isn't it set up for mono also i am wanting to know how a 5K taper for volume control would connect up any help appreciated GrahamComment
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You are just going to put the potentiometer in series with R38 as a variable resistor.Originally posted by Graham View PostComment
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